This invention relates to engine controls and more particularly to a control which will shut down an engine and shut off flow of fuel from the fuel tank in response to normal operating procedures or in response to emergency situations.
Typically, an engine is provided with a fuel system wherein fuel is delivered from a fuel tank through a throttle-controlled governor to the engine, the fuel system also including a solenoid-operated fuel valve in the fuel line to prevent flow from the tank when the engine is not in operation. In normal operation, the fuel valve is opened, the governor is moved by a throttle lever to fuel-on position and a start motor is energized to crank the engine and start it. With the engine in operation, the operator controls the speed thereof by adjustment of the governor. The engine is shut down by moving the throttle to fuel-off position so that no more fuel can flow through the governor to the engine. The fuel valve is turned off.
Additionally, solenoids are often used in conjunction with the governor to override the throttle and pull the fuel-rack of the governor to fuel-off position and thereby shut down the engine in case of emergency.
Further, engines, and vehicles in which such engines are used, are often equipped with a fire-extinguishing system which will release a suitable extinguishing fluid in the event of an engine fire. Some of such systems are manually operated while others have fire-sensors which cause the fire-extinguishing system to operate automatically in the event of a fire.
Such systems as generally described above have a number of deficiencies. Normal and emergency procedures oftentimes require different action on the part of the operator to control the fuel valve and engine shutdown. Fire-extinguishing systems are not tied in with the engine system, and require the operator to take affirmative action to shut down the engine and turn off flow of fuel to the engine compartment in case of a fire. Such action may not be taken at all if the engine is running unattended and a fire breaks out.
The solenoids presently used for the fuel valve and fuel rack also present problems. For example, the fuel-valve solenoid is designed to be energized as long as the engine is running, so that fuel will be continuously supplied to the engine. Normally, the flow of fuel through the valve will cool the solenoid. However, if the supply of fuel runs out, the cooling effect thereof will be removed and the power applied to the solenoid will often cause the coil to burn out.
Movement of the fuel rack to fuel-off position by solenoid actuation requires the use of a heavy-duty solenoid. The solenoids which are commercially available for this purpose typically have two coils in parallel, a low-resistance pull-in coil which develops the high power required to move the fuel rack to fuel-off position and a high-resistance hold-in coil which will hold the fuel rack in its fuel-off position once it has been moved thereto. A continued application of full power to the pull-in coil after it has completed its power stroke will cause it to burn out in a relatively short time. For this reason such solenoids are provided with contacts in series with the pull-in coil which open when the solenoid has pulled in, so that only the hold-in coil remains energized. Very often, however, trouble is encountered in the field in keeping the contacts properly adjusted. If the contacts open prematurely, before the solenoid has fully pulled in, the hold-in coil may not be able to hold the solenoid in, and it will drop out until the contacts close and the pull-in coil is re-energized. If the contacts fail to open on pull-in, the pull-in coil will remain energized and burn out.
Additionally, the use of solenoids presents problems in that the wiring harness to the solenoids may develop shorts to ground or the solenoids may be accidentally shorted by mechanics servicing the system. In either case, if power is being applied, or is thereafter applied to the solenoids, the shorts will adversely affect the functioning of the electrical system for the engine.